Method and apparatus for electrophotography

ABSTRACT

In an electrophotographic method in which an electrophotostatic latent image is obtained by uniformly charging and imagewise exposing an electrophotosensitive material and letting toner stick to the material according to the electrostatic latent image thereon, the electrophotographic method characterized in that the uniform charge on the electrophotosensitive material is varied according to the desirable contrast of the image to be obtained, and the exposure is controlled according to the surface potential, thereby obtaining a controlled contrast.

United States Patent [1 1 Matsumoto 1 Get. 2, 1973 [54] METHOD AND APPARATUS FOR 2,784,109 I 3/1957 Walkup ll7/l7.5 ELECTROPHQTOGRAPHY 2,277,013 3/1942 Carlson 355/3 X [75] Inventor: Seiji Matsumoto, Asaka-shi,

Saitama, Japan Primary ExaminerJohn M. Horan Armrney-Gerald J. Ferguson, Jr. [73] Asslgnee: Fu i Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: July 23, 1971 [57] ABSTRACT Appl. No.: 165,466

[30] Foreign Application Priority Data July 25, 1970 Japan 45/6473? [52] 11.8. C1. 355/3, 355/17 [51] lint. Cl 603g 15/04 [58] Field of Search 355/3, 17; 96/1 [56] 1 References Cited UNITED STATES PATENTS 2,965,483 12/1960 Byrne 96/1 1n an electrophotographic method in which an electrophotostatic latent image is obtained by uniformly charging and imagewise exposing an electrophotosensitive material and letting toner stick to the material according to the electrostatic latent image thereon, the electrophotographic method characterized in that the uniform charge on the electrophotosensitive material is varied according to the desirable contrast of the image to be obtained, and the exposure is controlled according to the surface potential, thereby obtaining a controlled contrast.

7 Claims, 8 Drawing lFigures PATENTEU 2 75 SHEET 2 BF 2 FIG. 6

INVE NTOR SEW MATSUMOTQ BY I M 8 m rr- FIG] hzwmmso wom zum5 zomco APPLIED VOLTAGE ATTORNEYg METHOD AND APPARATUS FOII ELECTROFIIOTOGAIPIIII BRIEF DESCRIPTION OF THE DRAWING FIG. I is a view showing gradation rendering property.

FIG. 2 is a view showing a preferred embodiment according to the present invention.

FIG. 3 is a view showing another preferred embodiment according to this invention.

FIG. 4 is a sectional view showing automatic exposure controlling means in another preferred embodiment according to the present invention.

FIG. 5 is a sectional view showing a clutching means for controlling system of charging quantity and for that of exposing quantity used in another preferred embodiment according to the present invention.

FIG. 6 is a view showing circuit construction of said exposure controlling system in said preferred embodiment.

FIG. '7 is a view showing circuit construction of high vOltage power source in above preferred embodiment.

FIG. 8 is a view showing property in relation to corona discharging voltage and electrode voltage in the present invention.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method and apparatus for electrophotography and particularly to a method and apparatus for controlling the charging exposure onto the electrophotoconductor, and the purpose of which is to correct the optical contrast in the copy of drawing, picture and/or photography to be copied, (hereinafter referred to originaL or contrast variations caused by flare of optical means to be used in copying.

In general, when an original is subjected to being copied, it is preferable to perform the copying by increasing the contrast of the original where the contrast thereof should be low and on the contrary, the copying is preferred to be carried out upon reducing the contrast of the original where the contrast thereof should be too high.

Shown in the FIG. I is gradation rendering characteristics according to the method of electrophotography showing an example of positive-positive method wherein the charging polarity onto the electrophotosensitive material is different from the polarity of the toner. A in FIG. I shows a characteristic curve wherein uniformly charged potential on an electrophotographic material is large and B thereof shows a characteristic curve where the potential is low. The curve A shows that the optical density of the image is largely charged against a little exposure variation, and the contrast there of is increased. Accordingly, it is appropriate for use where the contrast of image in an original is low. It is also suitable for compensating the decreased contrast caused by optical means used in image-exposure.

The curve B of the characteristic in low potential shows that gradation can be well realized in the copy against great variation of exposure when the potential is low and the contrast thereof becomes lower. Accordingly, if the contrast of the image in an original is high, in other words, if there is any particle difference of contrast, such an image can be well reproduced. The image thus copied by controlling the potential on the surface of the material according to the contrast on the original is provided with satisfactory contrast at all times. However, when the average density of the image on the original is preferred to be about the dotted line shown by C in FIG. I, the average exposure corresponding thereto is varied as shown by D and E in this figure according to each uniformly charged surface potential. Accordingly, it is necessary to vary the exposure (for example to change exposing time) to an electrophotosensitive material for obtaining an optimum density image according to the surface potentials. It is, however, extremely difficult to manually control each of these operations, and incorrect result is apt to be introduced in relation to the surface potential, thereby lowering working efficiency.

The present invention eliminates the aforementioned disadvantages. In the method where the electrophotosensitive material comprising electrophotoconductive insulating layer provided on electroconductive substrate is uniformly charged, exposed imagewise to form an electrostatic charge image thereon, and letting the charged toner stick selectively to electrostatic latent image and the toner image obtained is transferred to other paper or is fixed onto the electrophotosensitive material; the present invention is characterized by controlling the contrast of the electrostatic latent image by controlling the potential of uniform charging onto the electrophotosensitive material prior to imageexposure.

The apparatus according to the present invention is constructed so that the exposure may be automatically changed in connection with the surface potential of the material, and exposure can be controlled in order to obtain satisfactory images even when potential is varied for controlling the contrast of the toner image.

The present invention will be explained in more detail with reference to a preferred embodiment accord ing to the invention.

In FIG. 2, I is a high voltage power source and its output voltage is variable. 2 is corona discharging elec trode serving in applying the output of high voltage power source I, thereby generating corona discharging, and in charging electrophotosensitive material I passing thereby. The potential of this corona discharging varies according to the voltage to be provided, namely the surface potential of the electrophotosensitive material 4 can be improved as the voltage goes up and is charged less as the voltage goes down, and can be continuously changed. 5 is a shield, b is an endless belt having an electrophotosensitive material d thereon and driven to the direction of an arrow mark, and said electrophotosensitive material d is electrically charged thereby while it passes under the corona discharging electrode. 7 is a grounded brush contacting with the electroconductive substrate of the material. The electrophotosensitive material d charged thereon is carried to the exposing portion h, where it stays. Here the image of an original It is exposed imagewise through lens system Id. II and II are the light source for illuminating the original 9 and turned on or off by a switch I2. I3 is a timer to control illuminating time length which is varied according to voltage variation on the high voltage power source I. Accordingly, when the voltage of the high voltage power source I is varied in order to change the potential of the electrophotosensitive material I, the exposure is automatically varied according thereto. The potential variation of the high voltage power source I is being set in close relation to that of the exposure wherein the potential of the electrophotosensitive material 4 is changed according to the voltage change of the high voltage source l and the exposure against the variation of the potential of the electrophotosensitive material l becomes most optimum.

And in this case, the exposure control may be carried out not only by turning on and off of the light sources I1 and 11 but also by a shutter I4, etc. Shown in the FIG. 3 is an example wherein controlling method for exposure and the surface potential is changed, and in particular the distance between corona discharging electrode 2 and the surface of the electrophotosensitive material 4 are arranged to be varied. When the distance between the corona discharging electrode 2 and the electrophotosensitive material 4 is changed, electric current flowing into the electrophotosensitive material 4 varies, and the quantity of which will be increased when approached thereto and decreased when set away therefrom. Accordingly, the corona discharging electrode 2 is moved up and down by means of a system comprising a rack 15 and pinion 16 for changing the surface potential, and its motion is connected to the iris 17 of the lens system 10 according to the motion of the pinion l6 and the iris 17 is opened when the corona electrode 2 approaches the electrophotosensitive material 4, and is closed when apart therefrom, thereby making it possible to simultaneously compensate the exposure when contrast is changed according to the variation of the potential. A switch 12 of a timer 13 may be arranged to be off for a certain time length and can also be managed to make light or dark copies by manually increasing or decreasing exposing time starting from medium. In this case, even if the potential is changed to change contrast after changing the exposure time so that the copies may have more black color than medium, copy having stable blacky color can be obtained, as the exposure against the change of the potential is automatically changed.

FIG. 4 shows an example wherein this invention has been utilized for automatic exposing means for copying from the tansparent original 9. 18 is a light source and is turned on by means of a switch 12. 19 is phototube serving for measuring the light applied to the electrophotosensitiv material 4 by its reflecting light. It is also possible to measure the light by taking out a partial light for exposing by inserting a half mirror in the way of the optical means, 20 is a means to serve for closing the switch 12, when the quantity of light measured by the phototube 19 reaches the certain specified value. The quantity of light which enters the phototube I9 is restricted by the iris 17, by which the sensitivity of the phototube 19 in appearance is varied. As the more exposure is necessary when the potential of the electrophotosensitive material 4 is high, the light for exposing the electrophotosensitive material 4 is increased when the light to enter the phototube w is stabilized and the iris 17 is closed and sensitivity in appearance is decreased. The established quantity of light which enters the phototube 19 may also be varied by means of charging quantity without limiting the quantity of light entering the phototube 19. For example, a condenser (not shown in the figure) may be charged by the electric current from the phototube l9 and the established voltage make the charging control means actuate so that the exposing may be completed when the voltage charged on the condenser arrives at the predetermined value.

FIG. 5 shows a connecting mechanism of controlling charging means and the exposure, by which a pinion I6 is interengaged to a rack l5 serving for moving the corona discharging electrode 2 up and down and a pinion I6 is rotated by means of pulleys 2i and 2! and a belt 22. The pulley 21 is rotated by manually rotating a knob 23 by which the rack l5 and the corona discharging electrode 2 are moved up and down, thereby controlling the potential on the electrophotosensitive material (not shown in the figure) as described hereinbefore. And the rotation of the pinion I6 is simultaneously transmitted to the pinion 29 through the arms 24, 25 and 26 and rods 27 and 28 connecting these arms, resulting in rotating a ring 31 of the iris 30 and not only transmit the rotation of the pinion 16 but shifting the relation between the potential and the opening 32 of the iris 30 by moving the position of a fulcrum 33 thereof away from its moderate state, thereby obtaining a little more dark or light copy, and the exposure caused by the adjustment of contrast can automatically be compensated, as the transmitting means is still working as it is.

FIG. 6 shows an example of exposure controlling system. Switches 34 and 35 are used for turning on and off a light and connected to directly to the electric source of the light (not shown in the figure), and the actuation of these switches 34 and 35 control the exposure. 36 is means to serve for detecting the potential at both ends of the condenser 37, and when it becomes a predetermined value, the switch 35 is opened. 38 is an electric source for charging a condenser 37. A switch 39 is connected to the other switch 34 and closed when exposing is started. A switch 40 is opened when exposing is started and begins charging the condenser 37 through a variable resistor 41. The means 36 operates when the condenser 37 is charged to a predetermined voltage, open the switch 35 and stops the exposure. The time consumed until the voltage comes to a predetermined value after the start of charging this condenser 37 is decided by time constant which varies according to capacity and variable resistance value. And in this case, exposure is decided by changing the time constant, and potential and exposure can also be connected by handling the variable resistor fill by means of a handle 42 of the variable transformer 42 in the FIG. 7 as will be described hereinbelow. Accordingly, when the potential is varied to change the contrast of the image, exposure is also changed simultaneously, thereby obtaining an image easy to see or read at all times.

Shown in the FIG. 7 is an example of high voltage source. 43 is a well known electric source which is commercially available, 44 is a transformer and most of the voltage is obtained from the secondary side 45 thereof. 46 is a transformer, the voltage of which is supplied from the variable transformer 42, intended to obtain variable portion of voltage to the secondary side 47 thereof and connected in series to the transformer 44 at the secondary side. 48 is a diode for use of rectification and 49 is a condenser for smoothing use. The output 50 thereof is to be given to the corona discharge electrode 2. This output voltage is preferred to be 2 KV-NDKV, as corona discharge will not be generated when the output voltage is too low, and the problem of insulating must occur when it is too high. On the contrary if the rate of the variable portion is large, the corona current will be greatly varied with a slight change thereof, resulting in difficulty in handling. If the rate is too small, the range of change would become very small. The rate is preferable in 5 30 percent. It may also be in the range of 60 percent or more when a charging electrode is constructed so that the corona current flowing to the photosensitive material 4 is not affected with the fluctuation of the voltage of the power source (for example, a screen is provided between the corona discharging electrode and photosensitive material).

8 shows the relation between the voltage applied to the corona discharge electrode 2 and corona current, wherein the potential of the photosensitive material 4 is in proportion to the corona discharge current, F in the figure is its characteristic curve, and this curve shows that the current would not flow till the voltage applied to the electrode reaches a certain value and will be suddenly increased when the voltage goes over the value. If the equipment is used at the voltage at an average G, the voltage to apply the electrode is to be varied about this. The dotted line H is a contacting line of the characteristic curve F in voltage G and crosses lateral axis, the point of which is expressed to be I, and if the voltage I is supplied by a constant voltage source and the part .l more than the voltage is supplied by means of the variable voltage source, corona current can be obtained in proportion to the voltage of the variable source around the voltage G and the potential is able to be varied in proportion thereto. This does not necessarily have to be in proportionate relation, and instead the variable voltage may only be arranged to become great or small depending upon necessity.

As described hereinbefore, according to the present invention contrast of the image on the copy is controllable and precise exposure can be determined. As a method of varying surface potential, the potential can optionally be changed because it is possible to'control corona current flowing onto the photosensitive material 4 by changing the voltage to be applied to a screen. The electroconductive screen is provided between the corona discharging electrode 2 and electrophotosensitive material 4. The surface potential can be optionally selected by changing the speed of the belt 6 conveying the material 4, by changing a mechanical combination which transmit the rotation of a motor to the conveyor. The servo-motor may be used as a motor to carry the conveyor.

lln accordance with the present invention, as stated above, it is possible to change the surface potential of the photosensitive material 4 and to obtain optimum exposure corresponding to the potential and then it is possible to control the exposure and the potential for controlling the contrast of the image to be obtained. There would be no error in the amount of the exposure and the potential because the control is automatically carried out, and the working efficiency would be improved with remarkable results.

I claim:

ii. In an electrophotographic apparatus to obtain a visible toner image by uniformly charging, imagewise exposing an electrophotosensitive material and then applying toner, apparatus comprising a discharge means for uniformly charging the electrophotographic material including means for controlling the potential of the surface charge on the elctrophotosensitive material, and an image exposing means which controls, in response fo the operation of said surface potential controlling means and prior to said imagewise exposing, the amount of exposure to be used during said imagewise exposing in relation to the surface potential.

2. An electrophotographic apparatus as claimed in claim 2, wherein said discharge means has a circuit for varying the voltage to be applied to a discharging electrode.

3. An electrophotographic apparatus as claimed in claim ll, wherein said discharge means has a mechanism for varying the distance between a discharging electrode and the surface of the electrophotographic material.

4!. An electrophotographic apparatus as claimed in claim I, wherein said image exposing means has a timer for varying the exposure time.

5. An electrophotographic apparatus as claimed in claim ll, wherein said image exposing means has a circuit for varying the intensity of exposing lamp.

6. An electrophotographic apparatus as claimed in claim ll, wherein said image exposing means has a mechanism for controlling the transfer speed of the electrophotographic material through the image exposing station.

7. An electrophotographic apparatus as claimed in claim ll, wherein said image exposing means has an iris in the image exposing optical path, the opening of which is controlled by the surface potential. 

1. In an electrophotographic apparatus to obtain a visible toner image by uniformly charging, imagewise exposing an electrophotosensitive material and then applying toner, apparatus comprising a discharge means for uniformly charging the electrophotographic material including means for controlling the potential of the surface charge on the elctrophotosensitive material, and an image exposing means which controls, in response fo the operation of said surface potential controlling means and prior to said imagewise exposing, the amount of exposure to be used during said imagewise exposing in relation to the surface potential.
 2. An electrophotographic apparatus as claimed in claim 2, wherein said discharge means has a circuit for varying the voltage to be applied to a discharging electrode.
 3. An electrophotographic apparatus as claimed in claim 1, wherein said discharge means has a mechanism for varying the distance between a discharging electrode and the surface of the electrophotographic material.
 4. An electrophotographic apparatus as claimed in claim 1, wherein said image exposing means has a timer for varying the exposure time.
 5. An electrophotographic apparatus as claimed in claim 1, wherein said image exposing means has a circuit for varying the intensity of exposing lamp.
 6. An electrophotographic apparatus as claimed in claim 1, wherein said image exposing means has a mechanism for controlling the transfer speed of the electrophotographic material through the image exposing station.
 7. An electrophotographic apparatus as claimed in claim 1, wherein said image exposing means has an iris in the image exposing optical path, the opening of which is controlled by the surface potential. 